Digital offset color technology combines ink-on-paper quality with multi-color printing on a wide range of print media such as paper, foil and plastic substrates. Digital printing presses that use digital offset color technology offer cost-effective short-run printing, on-demand service and on-the-fly color switching.
A digital offset printing system works by using digitally controlled lasers to create a latent image in the charged surface of a photo imaging plate (PIP). The lasers are controlled according to digital instructions from a digital image file. Digital instructions typically include one or more of the following parameters: image color, image spacing, image intensity, order of the color layers, etc. Special ink is applied to the partially-charged surface of the PIP, recreating the desired image. The image is then transferred from the PIP to a heated blanket cylinder and from the blanket cylinder to the desired substrate, which is placed into contact with the blanket cylinder by means of an impression cylinder. Because of its role in transferring an image from the PIP to the ultimate substrate, the blanket may sometimes be referred to as an “intermediate transfer member” (ITM).
The ink is fluid on the heated blanket. The ink typically comprises pigment particles incorporated into a resin that is suspended in a carrier liquid. Typically, ink is applied to the blanket at a concentration of 20% (with the remaining 80% comprising carrier liquid). During the printing process, and due at least in part to the heating of the blanket, a large proportion of the carrier liquid is evaporated prior to transfer of the ink to the print medium.
A detailed description of the operation of a typical digital offset printer is described in Hewlett-Packard (HP) White Paper Publication, “Digital Offset Color vs. Xerography and Lithography”, for example. Specifically, an example of a digital printer that can be used to create the disclosed printed articles is HP's digital printing press Indigo Press™ 1000, 2000, 4000, or newer, presses, manufactured by and commercially available from Hewlett-Packard Company of Palo Alto, Calif., USA.